Loads a value from a byte array and performs a bitwise OR with that value. Values loaded from a byte array are sign extended to 32 bits before any any bitwise operations are performed on the value. Thus, if b[0] contains the value 0xff, and x is initially 0, then the code ((x << 8) | b[0]) will sign extend 0xff to get 0xffffffff, and thus give the value 0xffffffff as the result.

In particular, the following code for packing a byte array into an int is badly wrong:

int result = 0;
for(int i = 0; i < 4; i++) 
  result = ((result << 8) | b[i]);

The following idiom will work instead:

int result = 0;
for(int i = 0; i < 4; i++) 
  result = ((result << 8) | (b[i] & 0xff));